There is a conventional technique for detecting an internal state of a rechargeable battery such as a lithium ion secondary battery or a nickel hydride battery and visualizing a change of the inner state of battery, e.g., a reaction in the battery and a degradation of the battery.
It is known that the tiny elastic wave occurs inside the lithium ion secondary battery due to the change of the internal state during the charging or aging, such as a decomposition of an electrolyte, a mixture of moisture, a generation of bubbles involved in the formation of SEI layer on the surface of an electrode, a change of crystal structure caused by an intercalation of the lithium ion and a change of the interparticle distance.
JP H07-6795 A discloses the technique of detecting the elastic wave generated in the battery with a detection device including an AE (acoustic emission) sensor and an analysis device for analyzing the signal transmitted from the AE sensor, analyzing the feature of the elastic wave and of detecting the internal state of the battery. In this technique, analyzing the characteristics of the elastic wave detected with the detection device brings the detection for the change of the internal state of the battery such as the generation of bubbles accompanying chemical reaction and the breaking of the components due to the degradation.
However, the detection device of JP H07-6795 A does not consider the damping of the elastic wave traveling from the battery to the AE sensor, and thereby it is difficult to accurately detect the tiny elastic wave generated by the chemical reaction in the battery or the like.
The chemical reaction in the battery is closely related to the performance of the battery, so that it is required to locally find the distribution or strength of the chemical reaction in the battery during the manufacturing process. Especially, it is required to determine the location of the reaction and visualize the defects for solving the objectives due to the materials or design of the battery and the process or control system for manufacturing the same.
Unfortunately, the detection device of JP H07-6795 A may fail to accurately determine the location where the change (generation of bubbles, breaking and so on) occurs in the battery.
As mentioned above, it is difficult for the conventional detection device to accurately determine the change of the internal state inside the battery.